The present invention relates to a .alpha.-cyanoacrylate-based adhesive composition having good storage stability.
.alpha.-cyanoacrylates of general formula ##STR3## are rapid-setting adhesives which are suited for an extraordinarily rapid adhesion of a large number of materials like rubber, plastics, metal, leather and wood in various technical areas like machine construction, apparatus construction, electrical engineering, jewelery industry, watch-maker industry, household etc. The parts can be joined in an extremely short time of only a few seconds and the adhesive joints produced in this way have good mechanical strengths characteristics. These adhesive harden by anionic polymerization initiated by even small traces of extremely weak basic-acting compounds (Lewis bases) such as for example, water or methanol. Due to the extreme reactivity of these adhesives usually inhibition of premature polymerization which has an adverse effect on storage stability is required. Accordingly, in the past acidic gases like sulphur dioxide, nitrogen monoxide, carbon dioxide, hydrogen fluoride etc., have been added to these adhesives. Furthermore, proton acids including mineral acids like hydrochloric acid, sulphuric acid and polyphosphoric acid, anhydrides like phosphoric anhydride, sulfonic acids and carboxylic acids like acetic acid, itaconic acid and benzenesulfonic acid have been used as stabilizers. Typical patents relating to the aforementioned stabilizers are U.S. Pat. No. 2,765,332, U.S. Pat. No. 2,794,788, U.S. Pat. No. 2,756,251, U.S. Pat. No. 2,912,454, U.S. Pat. No. 2,926,188, U.S. Pat. No. 3,728,375, U.S. Pat. No. 3,993,678 and DE-OS No. 23 07 834. Reference is also made to U.S. Pat. No. 3,652,635, DE-OS No. 21 28 985, DE-OS No. 20 42 334, DE-OS No. 18 07 895 and DE-OS No. 21 18 701, which propose organic sulfonic acids, sulfonic anhydrides, aliphatic or aromatic sultons and aliphatic sulfocarboxylic anhydrides as stabilizers for .alpha.-cyanoacrylate-based adhesives.
However, gaseous stabilizers are only suited to a limited degree for effective stabilization of .alpha.-cyanoacrylates, since metering in the liquid adhesive is difficult and during storage undefined amounts can prematurely escape. When using higher concentrations of acidic gases or non-gaseous acids the curing rate of the .alpha.-cyanoacrylates rapidly decreases. On the other hand when using too low concentrations no sufficient stabilization is achieved.
It has now been surprisingly found that the above difficulties and disadvantages of the prior art stabilizers can be avoided or the stabilizing action can be improved by using as stabilizers certain sulfonic acid derivatives and preferably combinations of such sulfonic acid derivatives. It has also surprisingly been found that storage stability can frequently be still further improved by combining these stabilizers with compounds from the group consisting of (dihydroxy)-organylboranes and bis-(dihydroxyboryl)-derivatives.